Because there are some girls on this world who are vicious, evil creatures, and will start to haunt you, threatening to report you in if you don't do their bidding!
Unfortunately... that's not a joke
Oh I know. There are some, I work with 'em... who work the "sexual harassment" control policy at my job to get the men in trouble. HR has caught on and is taking steps to protect people, but the damage has been done.
After the blown out of proportion
Tailhook scandal the Navy endured in the early 1990's, sexual harassment policies in both the military and civilian world went out of control. Women would accuse men of harassment and *BOOM* automatic guilt and punishment. The common joke/comment is that it was the fat/ugly/lesbians (or a combination of all three) who were the ones abusing the policy. From that point on, innocent hugs, a pat on the back, or even innocent terms of affection (dear, hon -- oh yes, these are common in the South and contain zero sexual connotation) were thrown out the door for fear of punishment. It was nice to see that the courts wised up to this nonsense by the middle of the decade.